Topic: CB750 K3 cylinder block damage

[aejmeja1]

Hey folks,

I rebuilt the top end of my my K3 last winter. I've had no issues with the engine since the rebuild apart from it weeping oil from underneath the cylinder head (the weep is not bad, mostly cosmetic).

Tonight I pulled the head off to see what exactly is going on under there and discovered damage. There is a circular groove on the surface of the cylinder block where the weep is (see pic). I found the groove underneath the gasket. I have no idea what could have caused it... I was careful when putting the engine back together and cleaned all surfaces thoroughly.

How can i fix this? Do I have to have the cylinder block surface milled or can i simply use a sealant of some sort to fix it? Can i reuse the gasket (seemed fine)?

Another question: Do the black marks of my exhaust headers mean exhaust leaks (last pic)?

Thanks!

-J

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[BomberMann650]

Yes you had an exhaust leak.  Some Exhaust gaskets and proper torque will solve that.

The circle shouldn't contribute to an oil leak. Not having new o-rings fitted around the oil pathways will.

No sealant goo.

[ekpent]

 Most people would probably go with a new head gasket and the 6 rubber pucks and other o-rings while the top end is apart if you want to try and give it the best possible chance of being leak free. Some gasket sealant around the pucks are a good move also.

[aejmeja1]

Thanks for the responses! I'm currently looking at a cylinder block schematic on CSMNL and can't spot an o-ring that goes into that corner/oil passage? Seems only a dowel goes into that hole or am i reading the image wrong? It's also possible, since I dont know the history of my engine, that the cylinder block isn't K3. Theres no groove for an o-ring on the cylinder block surface...does something go into the dowel?

What could explain the leak if the damage to the cylinder block top surface isn't at fault?

Thanks!